1. Field of the Invention
The invention relates to a power output system that provides power to a driveshaft, a vehicle including the power output system, and a method of controlling the power output system.
2. Description of Related Art
Japanese Patent Application Publication No. 2001-41026 (JP-A-2001-41026) discloses an internal combustion engine including a HC adsorption apparatus provided upstream of a catalytic converter in an exhaust passage. The HC adsorption apparatus of this engine includes a main passage, a switching valve that opens and closes the main passage, and a bypass passage that bypasses the main passage, and a HC adsorbent that adsorbs hydrocarbon (HC) contained in exhaust gas is disposed in the bypass passage. The switching valve is coupled to a diaphragm of a diaphragm mechanism, and a variable pressure chamber of the diaphragm mechanism is connected to an intake manifold via a negative pressure feed line and a vacuum switching valve (VSV). When the VSV is turned on, a negative pressure produced through the operation of the engine is supplied to the variable pressure chamber of the diaphragm mechanism so as to deform the diaphragm, and the switching valve operates, in accordance with the deformation of the diaphragm, to close the main passage, so that the exhaust gas of the engine passes through the HC adsorbent in the bypass passage and then flows into the catalytic converter. When the VSV is turned off, the atmospheric pressure is introduced into the variable pressure chamber of the diaphragm mechanism via the negative pressure feed line, causing no deformation of the diaphragm, and the switching valve is placed in the fully opened state, so that the exhaust gas of the engine flows into the catalytic converter via the main passage, without passing through the HC adsorbent.
In the internal combustion engine as described above, when the catalytic converter has not been sufficiently warmed up, the negative pressure produced through the operation of the engine is used to switch the exhaust gas channel from the main passage to the bypass passage, so that hydrocarbon as an unburned component in the exhaust gas is adsorbed by the HC adsorbent in the bypass passage. After the catalytic converter is sufficiently warmed up, the exhaust gas channel is switched from the main passage to the bypass passage again, so that the adsorbed unburned hydrocarbon can be cleaned (i.e., converted into harmless substances) by the catalytic converter. However, the negative pressure cannot be produced while the engine is at rest or stopped, and, even if the engine is operated, a sufficiently reduced pressure may not be developed, depending on the operating conditions (load) of the engine. Thus, in the internal combustion engine as described above, switching of the exhaust gas channel from the main passage to the bypass passage may not be accomplished because of a shortage or lack of the negative pressure when the switching is to be done, and an unburned component, such as hydrocarbon, in the exhaust gas may be discharged to the outside without being converted into harmless substances.